Recently there has been considerable activity in the development of fiber reinforced resin leaf springs to replace the traditional steel leaf spring, as used in vehicles. Fiber reinforced resin leaf springs are normally formed by winding continuous strands of fibrous material impegnated with an uncured thermosetting resin about a pair of spaced bushings. After the desired number of layers have been wound on the bushings, the wound structure is molded under heat and pressure to cure the resin and form the leaf spring.
It is extremely important that when the spring is assembled to the vehicle, that there are no stress concentrations in the spring, for stress concentrations can cause rupture of the fibers and a loss of mechanical properties.
It has been found that when a fiber reinforced resin leaf spring is clamped to the vehicle axle using a conventional clamping mechanism, the gripping action is so strong that stress concentrations arise in the spring, particularly where the ends of the metal clamp engage the spring.
To eliminate stress concentrations at the clamping area, it has been proposed to enclose the central portion of the spring in an elastomeric jacket which serves to cushion the spring and prevent high stress concentrations during loading. However, the use of the elastomeric jacket prevents a conventional clamping mechanism from being used and requires special clamping equipment. Moreover, the elastomeric jacket adds to the overall cost of the clamping structure.
As a further problem, axial slippage can occur between the fiber reinforced resin spring and the clamping mechanism as the conventional U-bolts straddle the spring. Forming holes in the spring to receive the U-bolts, is not practical as it will sever the fibrous material and result in a loss of mechanical properties.